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Biomedical subjects

R Farré

Publications and source records attributed to R Farré.

At least 109 records · Page 6Linked to original sources
PubMed1991

Active inspiratory impedance and neuromuscular respiratory output during halothane anaesthesia in humans.

The aim of this study was to measure, in 11 patients with healthy lungs, active inspiratory impedance during anaesthesia. In addition, we recorded changes in inspiratory occlusion pressure at 100 ms (P0.1) and ventilatory pattern while awake and during anaesthesia with a mean inspiratory fraction (FI) of 0.017 halothane in O2. The total active inspiratory resistance and elastance values were 5.4 +/- 3.3 hPa.l.1.s and 29.9 +/- 6.2 hPa.l.1, respectively. P0.1 and the ratio between P0.1 and mean inspiratory flow (P0.1/(VT/TI)) increased 124% (p less than 0.001) and 68% (p less than 0.001), respectively, during anaesthesia. Respiratory frequency rose significantly from 12.2 +/- 1.5 (mean +/- SD) to 24.6 +/- 4.6 cycles.min-1, while tidal volume and inspiratory duty cycle lowered significantly from 0.599 +/- 0.195 l and 0.44 +/- 0.04 to 0.372 +/- 0.088 l (p less than 0.001) and 0.40 +/- 0.04 (p less than 0.05), respectively. Minute ventilation (VE) and VT/TI did not change significantly. During halothane anaesthesia with an FI:0.017, the increase in neuromuscular respiratory output appears to compensate for the increased mechanical load, thus resulting in maintenance of VE at levels similar to those of an awake state.

Adult↗
PubMed1990

Respiratory input impedance in anesthetized paralyzed patients.

Respiratory impedance (Zrs) was measured between 0.25 and 32 Hz in seven anesthetized and paralyzed patients by applying forced oscillation of low amplitude at the inlet of the endotracheal tube. Effective respiratory resistance (Rrs; in cmH2O.l-1.s) fell sharply from 6.2 +/- 2.1 (SD) at 0.25 Hz to 2.3 +/- 0.6 at 2 Hz. From then on, Rrs decreased slightly with frequency down to 1.5 +/- 0.5 at 32 Hz. Respiratory reactance (Xrs; in cmH2O.l-1.s) was -22.2 +/- 5.9 at 0.25 Hz and reached zero at approximately 14 Hz and 2.3 +/- 0.8 at 32 Hz. Effective respiratory elastance (Ers = -2pi x frequency x Xrs; in cmH2O/1) was 34.8 +/- 9.2 at 0.25 Hz and increased markedly with frequency up to 44.2 +/- 8.6 at 2 Hz. We interpreted Zrs data in terms of a T network mechanical model. We represented the proximal branch by central airway resistance and inertance. The shunt pathway accounted for bronchial distensibility and alveolar gas compressibility. The distal branch included a Newtonian resistance component for tissues and peripheral airways and a viscoelastic component for tissues. When the viscoelastic component was represented by a Kelvin body as in the model of Bates et al. (J. Appl. Physiol. 61: 873-880, 1986), a good fit was obtained over the entire frequency range, and reasonable values of parameters were estimated. The strong frequency dependence of Rrs and Ers observed below 2 Hz in our anesthetized paralyzed patients could be mainly interpreted in terms of tissue viscoelasticity. Nevertheless, the high Ers we found with low volume excursions suggests that tissues also exhibit plasticlike properties.

Adult↗
PubMed1989

Analysis of the dynamic characteristics of pressure transducers for studying respiratory mechanics at high frequencies.

Differential pressure transducers are commonly used to study respiratory mechanics at physiological frequencies as well as during external forcing at high frequencies. In the latter condition, measuring errors could occur if the input impedance of the pressure transducers is not sufficiently large with respect to that of the respiratory system. In this work we analysed the input impedance Z and the transfer function H of two common pressure transducers (Validyne MP-45 and Celesco LCVR) equipped with membranes of different sensitivities and with connecting tubes of different lengths. Z was measured by the tube method and H was measured by comparison with a flat-response pressure transducer. In agreement with the predictions based on a simple lumped-parameters model, we found that Z reached very low values, especially at the frequencies where H had a resonance peak. For instance, for the widespread Validyne MP-45 transducer (200 Pa) with connecting tubes of 16 cm length and 3.8 mm internal diameter a minimum of Z of 8300 Pa s litre-1 at 96 Hz was measured; at that frequency the amplitude of H attained a value of 3.1. Using the above transducer model we simulated the measurement of a rat input impedance up to 128 Hz using Validyne and Celesco transducers. With the Validyne MP-45 (200 Pa), equipped with the same connecting tubes as above, the computed error reached up to 50 per cent for the real part and 140 per cent for the imaginary part.

Animals↗
PubMed1989

A least squares algorithm to determine the mechanical time constant distribution of the lung during forced expiration.

A method to determine the mechanical time-constant distribution of the lung during a forced expiration manoeuvre is proposed. The method is based on a least squares algorithm constrained to give reasonably smooth non-negative solutions. The smoothing constraint was imposed by minimizing the second derivative of the distribution function in accordance with the physiological meaning of the time-constant distribution. Nevertheless, the obtained solution depends greatly on the relative weights of the two terms in the objective function to be minimized i.e., the error on the fit of the volume signal and the smoothness of the distribution function. To select the optimum smoothing weight, a criterion based on the stability of the reconstructed distribution shape was defined. The performance of the algorithm and that of the defined criterion were evaluated by using simulated signals of forced expired volume. The error of reconstructed distributions was quantified by means of the area enclosed between this distribution and the original one used to generate the simulated volume signal. The results obtained showed that for all the analyzed signals: (1) There is a value of the weight of the smoothing constraint which gives rise to a solution that is optimum in a least squares sense. (2) The proposed stabilization criterion enables us to approach this optimum solution from experimental signals.

Algorithms↗
PubMed1989

Respiratory input impedance during high frequency oscillatory ventilation.

Total respiratory input impedance (Zrs) measured by forced excitation may be computed easily from pressure and flow measurements recorded at the airway opening. The purpose of this paper was to analyse how the information provided by Zrs may be used for monitoring ventilatory mechanics during high frequency oscillatory ventilation (HFOV). We measured impedance (0.125-32 Hz) in six dogs, and in four dogs after infusion of histamine. We interpreted Zrs data in terms of a linear resistance-inertance-elastance (R-I-E) model to estimate the pressure decrease in the airways and the pressure amplitude in the alveolar region. We modelled airways non-linearities and analysed their effect at high flow oscillation amplitudes. We concluded that Zrs measurements may be useful to monitor ventilatory mechanics and to determine the optimum settings of the ventilator during HFOV.

Animals↗
PubMed1989

A correction procedure for the asymmetry of differential pressure transducers in respiratory impedance measurements.

The usual setup for measuring respiratory input impedance requires a differential pressure transducer attached to a pneumotachograph. As, up to now, no data correction procedure has been devised to account for transducer asymmetry, a highly symmetrical transducer is required to obtain reliable impedance data. In this communication, a general model for the measuring system is presented. Its main feature is that differential pressure transducers are modeled as two input-one output systems. From the theoretical model, we defined a dynamic calibration and data correction procedure. This was tested using highly asymmetrical transducers (common-mode rejection ratio between 45 and 27 dB) to measure the impedance of two respiratory analogs. The latter were linear resistance (R), inertance (I), compliance (C) series models simulating a normal subject (R = 3.47 hPa.s.l-1, I = 1.45 Pa.s2.l-1, C = 18.6 ml.hPa-1) and an obstructive patient (R = 11.15 hPa.s.l-1, I = 1.28 Pa.s2.l-1, C = 18.5 ml.hPa-1). Results obtained applying the devised procedure (errors in R, I, and C always less than 4 percent) show that respiratory input impedance can be adequately measured if data are corrected for transducer asymmetry.

Airway Resistance↗
PubMed1989

Lung impedance in healthy humans measured by forced oscillations from 0.01 to 0.1 Hz.

Lung impedance was measured from 0.01 to 0.1 Hz in six healthy adults by superimposing small-amplitude forced oscillations on spontaneous breathing. Measurements were made with an almost constant-volume input (160-180 ml) or with an almost constant-flow input (20-30 ml.s-1). No significant difference was found between the two conditions. Lung resistance (RL) sharply decreased from 0.97 kPa.l-1.s at 0.01 Hz to 0.27 kPa.l-1.s at 0.03 Hz and then mildly to 0.23 kPa.l-1.s at 0.1 Hz. Lung effective compliance (CL) decreased slightly and regularly from 0.01 Hz (2.38 l.kPa-1) to 0.1 Hz (1.93 l.kPa-1). The data were analyzed using a linear viscoelastic model adapted from Hildebrandt (J. Appl. Physiol. 28:365-372, 1970) and complemented by a Newtonian resistance (R): RL = R + B/(9.2f); CL = 1/(A + 0.25B + B.log2 pi f), where f is the frequency and B/A is an index of lung tissue viscoelasticity. A good fit was generally obtained, with an average difference of 10% between the observed and predicted values. The ratio B/A was not affected by the breathing and was 10.6 and 13.6% in the constant-volume and constant-flow conditions, respectively, which agrees with Hildebrandt's observations in isolated cat lungs. R was systematically larger than the plethysmographic airway resistance, suggesting that lung tissue resistance might also include a Newtonian component.

Adult↗
PubMed1989

Recording pressure at the distal end of the endotracheal tube to measure respiratory impedance.

To minimize the flow-dependent effects caused by an endotracheal tube during impedance measurements, we recorded pressure inside the tube at its distal end. We used a commercial endotracheal tube with a lumen built into its wall with the opening located near the outlet of the tube. We characterized the effect of the tube by means of an effective transfer function (H). We measured H from 0.25-32 Hz on a mechanical analogue by using pseudorandom excitation with different peak-to-peak flow amplitudes (Vpp). For an 8 mm internal diameter (ID) endotracheal tube the modulus of H measured with Vpp 0.2 l.s-1 was 1.00 at 0.25 Hz and increased with the frequency to 1.40 at 32 Hz. The phase factor was close to zero (less than 5 degrees) over the whole frequency band. The modulus of H changed less than 5% and the phase factor less than 3 degrees when Vpp was increased from 0.2 to 0.8 l.s-1. We evaluated the method on five mechanical analogues with increased resistance or elastance and with a different tracheal area. The mean normalized distance in the complex plane over the whole frequency band (dz) between the analogue impedance and the estimated value from intubation was always less than 5%. Finally, the method was tested on an active analogue which superimposed a high-amplitude (up to 1.4 l.s-1 peak-to-peak) low-frequency (0.25 or 0.33 Hz) sinusoidal flow onto excitation: dz was always less than 4.3%.

Airway Resistance↗
PubMed1988

Algorithms for dosage and therapeutic monitoring of theophylline.

Theophylline is widely prescribed in Spain. Because this drug has a narrow therapeutic range and high interindividual pharmacokinetic variability, it is essential to adapt the dosage to each patient. In order to simplify the drug individualization we are proposing three algorithms to apply to intravenous loading and maintenance doses and to oral doses. The initial recommended dosages have been established using the pharmacokinetic parameters obtained from patients treated with theophylline in our hospital. Because the pharmacokinetic behavior of theophylline may be different in other populations, dosage requirements may not be the same. A minimum number of blood sample collections is proposed in an attempt to improve the cost-benefit relationship in theophylline therapy.

Adolescent↗
PubMed1986

Cobalt content of foods and diets in a Spanish population (short communication).

The WHO Expert Committee on Food Contaminants has pointed out the need of determining the content of foods in trace elements in order to ascertain their contribution to the total intake of oligoelements through the diet. Since the contents in trace elements depend on the environmental features, it is necessary to carry out systematic determinations of trace elements in foods of local origin in order to know the exposure level of population. This work intends to study the cobalt contribution through the diet. The element intake is calculated from the cobalt content in raw foods after elimination of the non-eatable moiety by flame atomic absorption spectroscopy, after formation of a chelate with ammonium pyrrolidine dithiocarbamate (APDC) and extraction with 4-methyl-2-pentanone (MIBK) according to a procedure developed and verified in a previous paper.

Adolescent↗
PubMed1986

[Effectiveness of rectal metromidazole in acute infantile appendicitis].

Thirty two consecutive children who underwent surgery for suspected acute appendicitis, were treated with prophylactic metronidazole suppositories. A serum sample was taken at surgery to determine the serum concentration of the drug. After a preoperative dose of 15-20 mg/kg the minimal bactericidal concentration was achieved in almost all cases at the time of anesthetic induction. This drug showed an optimal biodisponibility when used rectally and no side-effects was noted. Neither a wound-infection, nor a wound-sepsis was reported and a satisfactory outcome was registered. We conclude that rectal dosing with metronidazole is effective for prophylactic wound infection in acute appendicitis.

Administration, Rectal↗
PubMedDate not supplied

Atomic absorption spectrophotometric determination of chromium in foods.

A method is reported for determination of chromium in foodstuffs. Organic matter is digested with nitric acid, followed by oxidation to Cr(VI) and extraction with methyl isobutyl ketone (MIBK) after HCl addition. Chromium determinations are performed by flame absorption spectroscopy. Absence of interferences is verified and recovery tests are performed on food samples. Quantitation limit (3.8 ng/mL), accuracy (NBS Standard Reference Material 1,573 Tomato Leaves, 4,500 +/- 500 ng/g, found 3,860 +/- 409 ng/g), and precision (CV for vegetable matrix = 9.05%, CV for animal matrix = 14.95%) of the procedure are evaluated.

Chromium↗
PubMedDate not supplied

Atomic absorption spectrophotometric determination of cobalt in foods.

A method is described for the determination of cobalt in foods. After wet digestion, iron in the sample is removed by liquid-liquid extraction, and cobalt is isolated and extracted. Final determination is done by flame atomic absorption spectrophotometry. Analysis of NBS reference materials by this procedure gives results in close agreement with certified values. The limit of quantitation is 4.3 ng/mL. Recovery studies and analysis of standard materials show that this method is reliable.

Cobalt↗